Vehicle alarm system

ABSTRACT

A sensitive current detector includes the vehicle ammeter and is responsive to current therein to activate a first pulser which sets a monostable multivibrator which activates another pulser having an output to the vehicle horn relay to sound the horn at a 2 cycle per second (Hz) frequency. The monostable multivibrator resets after 1 minute of sounding of the horn to deactivate the horn unless the current detector continues to sense current. A delay timer responds to a key operated switch or a remote disable switch to inhibit, for 15 seconds, activation of the second pulser by the monostable. The monostable multivibrator can also be set by mechanically operable switches.

B United States Patent 1 [111 3,748,494 Nine 1 July 24, 1973 4] VEHICLE ALARM SYSTEM 3,422,398 1/1969 Rubin 307/10 AT Inventor: Philip L. Nine, Indianapolis, Ind. 3,531,793 9/1970 Shottenfeld 340/274 X [73] Assignee: Curtis Dyna-Products Corporation, primary Examiner ]ohn Heyman Westfield, Ind. Attorney-Woodward, Weikart, Emhardt & Naughton [22] Filed: Apr. 14, 1971 21 Appl. No.: 134,033 1 AB TRACT Rehted S Application Data A sensitive current detector includes the vehicle am- [62] Division of Ser No 847 922 Au 6 1969 Pat No meter and is responsive to current therein to activate 3 605 087 a first pulser which sets a monostable multivibrator which activates another pulser having an output to the 52 us. Cl. 307 235, 307/237, 307/10 AT, vehicle relay Shhd the horn a 2 cycle P 307/10 R, 340/63, 307/247, 307/273 second (Hz) frequency. The monostable multivibrator 51 Int. Cl. H03k 5 20, H02h 3/00 resets after 1 minute of Sounding of the horn deacti- [58] Field of Search 307/10 R, 10 AT, the horn the current detector continues to 307/10 LS, 237 235 247 275; 340/274, 63 sense current. A delay timer responds to a key operated 64 switch or a remote disable switch to inhibit, for 15 sec onds, activation of the second pulser by the monosta- [56] References Cited ble. The monostable multivibrator can also be set by UNITED STATES PATENTS mechanically operable switches.

3,378,695 4/1968 Marette 307/237 5 Claims, 2 Drawing Figures PAIEMEDM 3.748.494

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cmsm' ALARM DETECTOR PULSE? SWITCH n PULSEFZ TIMER Z2 VEHICLE ALARM SYSTEM This is a division of application, Ser. No. 847,922, filed Aug. 6, 1969.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to alarm systems, and more particularly to a comparatively simple and inexpensive, but reliable system which is responsive, with high sensitivity, to electric current usage in a vehicle electrical system.

2. Description of the Prior Art Alarm systems of considerable variety are known in the art. Yet there remains to be solved the specific problems created by new and different environments for alarms, new technology, and the ever present demand for lower cost and improved performance.

Vehicle alarm systems are known which respond to mechanical stimuli such as the opening of a window, or a door, or. a hood. Another is known which uses an inductive coupling to a battery cable to initiate an alarm. Yet these devices have aspects which are considered disadvantageous in certain respects. It is an object of the present invention toprovide a system meeting requirements as outlined above and providing a combination of features advantageous over systems currently known.

SUMMARY OF THE INVENTION- Described briefly, in a typical embodiment of the present invention, solid state circuitry is employed throughout and includes a two-transistor constant current source whose output is varied in response to small current usage in the vehicle electrical system, as by the illumination of a courtesy lamp upon opening a door, for example. The change in output is effective, after a predetermined initial delay, to set a multivibrator to initiate an alarm pulser, the pulser remaining activated to pulse the vehicle horn during the period of the monostable multivibrator prior to automatic reset thereof. A key switch is employed through appropriate time delay means to activate and deactivate the alarm system. A remote disabling switch and associated delay circuitry facilitates short term disablement of the system when desired by the proprietor thereof.

BRIEF DESCRIPTION OF THE DRAWINGS "FIG. 1 is a block diagram of a typical embodiment of the present invention.

FIG. 2 is a schematic diagram thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, and particularly the block diagram of FIG. 1, the current detector 11 is coupled to the ammeter 12 of the vehicle and responsive to current therein, afterthe key lock operated switch 13 is closed, to activate the pulser 14 which, in turn, activates the alarm switch 16. Thesteady state output of the alarm switch, once set by the pulser l4, activates the alarm pulser 17 producing a pulse output to the vehicle horn relay coil 18, to pulse the vehicle horn 19.

A delay timer 2] connected to the alarm switch 16 is activated initially upon activation of the alarm system by closing the key switch 13 to permit closing of doors or'trunk lids or other activity by the proprietor of the system (owner of the car, for example) for a predetermined period of the order of 15 seconds, for example. The delay timer may also be activated by closure of a disable switch 22 at any time after the alarm system has been activated by the key switch. Such a disable switch can be amagnetically operated reed switch located at some secret location on the vehicle. This permits temporary (15 second) disablement of the system by the proprietor to permit his entry into the vehicle, for example. Such a reed switch could be operated by temporarily holding a magnet near the switch as, for example, adjacent a corner of the windshield. In either event, the delay timer disables the alarm switch 16 from activating the alarm pulser for a period of approximately 15 seconds.

A mechanical switch 23 is provided and connected to some vehicle component such as a hood 24, for example, operation of this switch being effective to activate the alarm switch 16.

Referring now particularly to FIG. 2, the B+ terminal of the vehicle battery is connected to the supply line 26, and return line 27 is connectable to battery ground 28 through the key-operated switch 13. A variety of suitable key-operated locks can be employed for manually opening or closing this switch. The horn relay 18 is shown with one side thereof connected to 8+ and the other side thereof connected through the normally open manually operable horn ring switch 29, the other side of which is at ground 28. One side of the vehicle ammeter is connected to 8+ through line 26, the other side being connectable to ground 28 through any one of a variety of vehicle equipment items designated generally as 32. These can be courtesy lights as indicated above, a radio, ignition primary circuit, or parking light, for example.

As indicated above, the alarm system is activated or armed by closing the key lock operated switch 13. Although there is an initial delay thereupon initiated, prior to the time when the horn can be sounded by the alarm system, that feature will be described hereinafter. For the present, the various blocks appearing in the block diagram and described generally above, will now be described in more detail.

The current sensing circuit 1 l-includes a two transistor constant current source with the automobile ammeter 12 or suitable current shunt as a part of the current determining elements. The base-emitter voltage of the diode-connected transistor 0;, (V is determined by the current thru 0,. This voltage appears across the base-emitter junction of Q and across the emitter resistor, R of Q and the ammeter. The base-emitter voltage of 0 (V is determined by the current thru 0 If the current thru 0, is less than the current thru Q then V, will be less than V This voltage difference is predictable and is about millivolts (mv) per decade of current difference. The voltage across the emit ter resistor and the ammeter is V V and the current thru Q, a V V /R, R, when R, is the meter or shunt resistance.

When current flows thru the ammeter from the battery, (eg. a light is on), the voltage drop across the ammeter will increase. The current, I, will decrease since I V V I R IR R,, The decrease of current, I, will cause a corresponding decrease in voltage at the collector of Q and will forward bias switching transistor Q Resistor R is a variable resistor for adjustment purposes, and resistor R may be on the order of I ohm for appropriate sensitivity. Diodes CR and CR are employed for temperature compensation for the switching transistor Q Transistor O is normally off when there is no current flow through the ammeter 12. It will turn on when the battery current increases to about 100 milliamperes (ma). When transistor is turned on, it turns on the gating transistor Q which begins charging capacitor C through resistor R The unijunction transistor Q will be fired when capacitor C is charged, and will thereupon produce a pulse output at 33. Therefore, in this combination we have an astable multivibrator in the form of a unijunction sawtooth generator. The frequency is about 0.5 pulses per second. The charging time of capacitor C is established at approximately 2 seconds in order that it be long enough to permit electric winding of the vehicle clock without firing the unijunction transistor.

The monostable multivibrator 16 includes transistors Q9 and Q and transistors Q8 and Q The timing thereof is determined by capacitor C and resistor R so that when the multivibrator is set, it will remain in the set condition for approximately 1 minute and it is during this 1 minute period that the alarm is sounding, as will soon be described. Then it will automatically reset.

In its first normal stable state, the multivibrator 16 has transistors Q and Q conducting. However, upon application of a pulse through capacitor C from the pulser 14 to the base of transistor Q to set the multivibrator, the base of Q is driven below ground, turning off these transistors and producing a positive going output signal at 34. In addition to the vehicle ammeter current responsive pulser means of setting the monostable multivibrator, it can be set by closure of the normally open mechanically operated switch 23, grounding the base of transistor Q and turning off this one and thereby transistor 0, to produce the signal output at 34. Closure of the switch 23 could be effected by the opening of the vehicle hood, a door, a window, the luggage compartment, or some other mechanical activity.

When the multivibrator output signal appears on the output line 34, unless it is inhibited from activating the alarm by means of the circuitry 21, it is applied to the base of gating transistor Q to tire the second unijunction astable multivibrator O which produces a 2 Hz pulse to the base of transistor Q which, through resistor R connected to the base of power transistor Q drives the latter. The power transistor Q grounds the one side of the vehicle horn relay to sound the horn. The frequency of the astable multivibrator using the unijunction Q establishes the frequency at which the horn is sounded, giving the beeping or pulsating sound. This astable multivibrator will run until the monostable multivibrator l6 automatically resets itself, the timing of which is determined by the resistor R and capacitor C The 2 Hz frequency of the alarm pulses is determined by capacitor C and resistors R and R2].

It was mentioned above that the monostable multivibrator will automatically reset in approximately l minute, thus terminating the beeping of the vehicle horn. However, if current continues to flow in the vehicle ammeter, it will continue to be sensed by the sensor of the present invention, thus causing the pulser 14 to continue to supply the sharp pulses to the base of transistor Q Consequently the monostable will be triggered again each time it resets, so long as battery current continues to flow through the ammeter l2. Similarly, so long as the mechanical switch 23 remains closed, the monostable multivibrator will not reset or, if it does reset, will immediately be restarted and thereby continue to produce the needed output to the gating transistor Q to keep the alarm pulser running.

If the key lock operated switch 13 is located inside the vehicle, it is desirable to provide a certain period of delay between the time it is closed to arm the alarm system, and the time the system becomes armed. For this purpose, the initial delay circuitry 21 is provided. Transistor Q10 is connected between the monostable multi output 34 and ground. When transistor O1, is on" it will hold Q in saturation, thus inhibiting operation of the alarm pulser by the monostable multi l6.

Q, is biased on" when transistor Q12 is off and will turn of when Q turns on. When the key switch is turned on, (i.e., closed) Q is turned on and Q is off. Capacitor C. starts charging thru resistor R As soon as Zener diode CR is forward biased (about 6V), Q turns on, turning off On and thereby Q and the monostable multivibrator 16 will no longer be inhibited from operating the alarm pulser.

Where the key operated switch is located inside the vehicle, it is desirable to provide some means for the operator to disarm the alarm system while he gains access to the interior of the vehicle to open the key switch. One example of means useful for this purpose is the provision of a magnetic reed-operated switch near one of the windows, such as the windshield for example. This switch can be operated by holding a magnet near it and such a switch can be employed as the remote disable switch 22 of the circuitry. Closure of this switch momentarily will discharge capacitor C whereupon the threshold required by the Zener diode CR for keeping transistor Q on will be removed. Thus transistor Q will turn off and transistors O and thereby Q will again be turned on, and inhibit operation of the alarm pulser gate Q by the monostable multivibrator 16.

When the remote disable switch reopens after its momentary closure, capacitor C will again start charging and, when the threshold of the Zener diode is reached, transistor Q will turn on to remove the inhibiting of the monostable multivibrator operation. In either event of utilization of the circuitry 21, the inhibit time is about 15 seconds. In normal usage, after the operator of the vehicle disables the alarm system with the remote disable switch, and enters the vehicle, he will utilize the key switch to disable the system. Diode CR permits capacitor C to discharge immediately when the key switch is turned off to disarm the system.

From the foregoing description, it will be recognized that the present invention has a variety of beneficial features. These include sensing electric current drawn from the battery to sound the alarm, turn-on delay, automatic reset, remote disabling, a pulsating alarm, mechanical switch activation as desired, and alarm delay. The sensor can be adjusted to be immune to steady state currents through the ammeter up to a certain level, if desired, and respond to any currents exceeding that level.

The invention claimed is:

l. A sensing method for an alarm system and comprising the steps of:

applying a potential to a diode-connected transistor to provide a first current therein establishing a desired base-emitter voltage therein,

applying the base-emitter voltage of said diodeconnected transistor across a series combination of the base-emitter junction of a second transistor, an impedance, and a portion of a vehicle electrical system, thereby normally maintaining a forward bias on said second transistor to keep it normally conducting,

and applying a potential across the combination of said series combination in series with a second impedance,

and thereby establishing at said second impedance a voltage dependent on the current in said series combination as influenced and varied by change of resistance of said portion of said vehicle electrical system.

2. In an alarm system for a vehicle electrical system,

a sensor comprising:

a constant current source having a normally conducting diode-connected biasing transistor with the emitter-collector path thereof in series with a first impedance means across an energy supply, and a normally conducting current source transistor having its base coupled to the collector of said biasing transistor and normally forward biased by the emitter-base voltage of said biasing transistor, and having its emitter-collector path coupled in series with a second impedance means and a portion of said vehicle electrical system in a circuit with said eny pp y the said current source transistor having an output conductor coupled thereto to produce an output signal thereon.

3. The alarm system of claim 2 wherein:

said vehicle electrical system portion is one in common circuit relationship with a plurality of electrical devices of the vehicle electrical system.

4. The alarm system of claim 3 wherein:

said sensor includes in the series coupling of the emitter-collector path of said current source transistor and said second impedance means and said electrical system portion in said circuit, third impedance means to establish the level of said sensor signal output in response to current flowing in said electrical system portion.

5. The alarm system of claim 4 wherein:

said electrical system portion is resistance of an ammeter in series with said energy supply and the load of at least one of said electrical devices, said resistance rising upon flow of current from said energy supply through said load to reduce current in the emitter collector path of said current source transistor to thereupon change the level of said sensor signal output. 

1. A sensing method for an alarm system and comprising the steps of: applying a potential to a diode-connected transistor to provide a first current therein establishing a desired base-emitter voltage therein, applying the base-emitter voltage of saiD diode-connected transistor across a series combination of the base-emitter junction of a second transistor, an impedance, and a portion of a vehicle electrical system, thereby normally maintaining a forward bias on said second transistor to keep it normally conducting, and applying a potential across the combination of said series combination in series with a second impedance, and thereby establishing at said second impedance a voltage dependent on the current in said series combination as influenced and varied by change of resistance of said portion of said vehicle electrical system.
 2. In an alarm system for a vehicle electrical system, a sensor comprising: a constant current source having a normally conducting diode-connected biasing transistor with the emitter-collector path thereof in series with a first impedance means across an energy supply, and a normally conducting current source transistor having its base coupled to the collector of said biasing transistor and normally forward biased by the emitter-base voltage of said biasing transistor, and having its emitter-collector path coupled in series with a second impedance means and a portion of said vehicle electrical system in a circuit with said energy supply, the said current source transistor having an output conductor coupled thereto to produce an output signal thereon.
 3. The alarm system of claim 2 wherein: said vehicle electrical system portion is one in common circuit relationship with a plurality of electrical devices of the vehicle electrical system.
 4. The alarm system of claim 3 wherein: said sensor includes in the series coupling of the emitter-collector path of said current source transistor and said second impedance means and said electrical system portion in said circuit, third impedance means to establish the level of said sensor signal output in response to current flowing in said electrical system portion.
 5. The alarm system of claim 4 wherein: said electrical system portion is resistance of an ammeter in series with said energy supply and the load of at least one of said electrical devices, said resistance rising upon flow of current from said energy supply through said load to reduce current in the emitter collector path of said current source transistor to thereupon change the level of said sensor signal output. 